A unicontrol high-frequency radio direction finder

The Bureau of Standards was asked to develop for the United States Coast Guard, a simple type of radio direction finder which should function on 2100 kc. (143 m). Such a device enables a ship so equipped to locate another ship readily. A paper under the above title, by F. W. Dunmore, (Scientific Paper No. 525 of the Bureau of Standards) describes the development of such a direction finder and its installation on a Coast Guard patrol boat. The direction-finder coil consists of four turns of ignition cable, wound on a 20-in. frame. It is installed over the pilot house and rotated from below. A tuning unit and coupling transformer have been designed so that the direction-finder coil may be used on the ship's receiving set without changing its tuning adjustments, which are locked in the 2100-kc. position. A special form of automatic balancing condenser, operated by a special cam rotating with the direction-finder shaft, is incorporated in this instrument. Thus a clear minimum may be obtained at all angular positions of the coil without manual operation of the balancing condenser. The controls necessary when taking a bearing are in this manner reduced to one that of rotating the direction-finder coil to obtain the minimum signal.